1. Field of the Invention
This invention relates to the field of regulators for gaseous flow, and in particular flow regulators for solid fuel combustion devices such as wood stoves.
2. Description of the Prior Art
A number of devices have been conceived in which thermostats are connected in one manner or another to draft regulators on flues. Such devices have never become popular, and the usual flue is not equipped with any thermostatic member. The normal barometric or pressure-driven flue vent, having no thermostatic control, comprises a flapper member which is pivotally disposed at the mouth of the vent passageway, leading to the flue.
The connection between the combustion gas flue and the vent passageway is normally that of a "T", the vent tube meeting the flue at a right angle. Commonly, the vent is disposed horizontally and the flue vertically. The flapper valve for the vent is mounted across the vent opening to pivot upon a horizontally-disposed pivot bar. The pivot bar is usually located off-center, that is somewhat above the geometric midpoint of the flapper, whereby the flapper assumes a vertical position, completely blocking the flue vent, unless acted upon by air pressure.
Heated gases passing upwards through the flue create a pressure differential between the free air and the combustion exhaust at the inside of the flue, that is, a pressure differential across the flapper valve. The pressure differential opens the flapper valve, permitting free air to enter the flue through the vent passageway and to be carried along with the combustion gases. In theory, air from the vent satisfies momentary deficiencies in flow. The draft through the flue is thereby made less variable, allowing more dependable flow and more complete combustion of the fuel.
Several devices have been conceived which are intended to interface with such off-center balanced flapper valves. Such devices, for example, U.S. Pat. No. 2,401,553--Crew and 3,087,677--Patrick purport to allow the flapper valve to operate relatively freely, influenced, but not fully controlled, by a bimetallic thermostat member. Although such thermostatic control means may be useful for smoothing out variations in flue flow, thought necessary in the prior art, such devices fail to actually control the flow of gases in the flue. Rather, the flue vent is subject to the control of exhaust gases instead of the source of control therefor. Prior art flue vents are positioned by action of the draft in the flue. Thermostatic members may be included to influence flow, but the flap remains subject to flow in the flue, rather than vice-versa. Accordingly, the prior art fails to employ the flue vent to control the rate of combustion by controlling the egress of hot gases.
The present invention seeks to actually control the rate of combustion upstream of the flue by directly and rigidly controlling the passage of air through a flue vent equipped with a flapper valve member. The flapper valve of the invention is preferably mounted on a centered pivot, but may be conventionally mounted and balanced by an adjustable member. In any event, according to the invention variations in gas flow in the flue have little or no effect on the position of the flapper valve. The rate of exhaust flow does not control the flow of room air through the vent tube, and into the flue.
A bimetallic thermostat member is directly attached to the centrally pivoted flapper by means of a rigid linkage. The thermostat is preferably a coil of bimetallic material which expands when heated, forcing the vent flap closed or open as the flue is cooled or heated, respectively, by combustion gases.
The particular temperature at which the flap is positioned at a given angle may be initially adjusted and locked by means of a length-adjustable linkage member and/or, an indicator and scale arrangement may be included in the thermostat mounting, allowing the operating temperature to be set as desired at any particular time. The flap may also be locked shut in order to confine smoke while first lighting the stove, then allowed to open once a draft is established.